Solvent dewaxing process



Filed July 28. 1958 mzON wz-J-Omo x43 States atet f This invention relates to a method for the solvent de- Waxing of petroleumvhydrocarbon lubricating oil fractions. More particularly, this invention relates to an improved method for the solvent dewaxing of petroleum hydrocarbon lubricating oil fractions wherein an enhanced rate of recovery of dewaxed oil is obtained, Still further, this invention relates to an improved combination process for the simultaneous dewaxing of oil and deoiling of Wax.

Paraiiinic petroleum hydrocarbon fractions which are suitable for use as base materials in the compounding of motor oils will normally contain a signicant amount of wax which must be removed if a satisfactory motor oil is to be obtained. The Wax is normally removed from such feed stocks in a continuous process by fractional crystallization of the wax from a solution of the feed stock in a dewaxing solvent. In order to remove the wax economically, it is desirable to providefor as high a ratio as possible of recovered dewaxed oil to dewaxing solvent. This is necessary in order to provide for a minimized plant construction cost, plant .operation cost, and plant maintenance cost.

In addition, it is frequently desirable to treat the wax resulting from a de-waxing operation in order to remove oil impurities therefrom to thereby provide a purified Wax which is useful in commerce.

It has been discovered in accordance with the present invention that the amount of dewaxed oil obtained in a continuous process `for a given solvent inventory may be substantially increased by a continuous process wherein a solution of a waxy feed stock in dewaxing solvent is chilled to an extent sufcient to form a pumpable slurry of about to l5 volume percent of Wax 'crystals in a mother liquor comprising the solvent-oil solution, wherein the slurry is turbulently isothermally filtered to yan extent suicient to remove from about 20 to 60 volume percent of the mother liquor, wherein the concentrated slurry is diluted with an additional quantity of solvent suicient to provide a second slurry having about the same concentration of Wax crystals as the original slurry and subjecting the second slurry to a second turbulant isothermal filtration step to obtain a recycled filtrate fraction and a concentrated wax fraction, the recycled filtrate fraction being admixed with the initial wax slurry prior to the initial turbulent isothermal ltration step.

In accordance with one aspect of the present invention, further advantages are obtained in that a ilexible process is provided wherein several grades of dewaxed oil of controlled pour point may be obtained or wherein a single grade of dewaxed oil is obtained having a pour point controlled by the selective rejection of all or a portion of at least one recycle fraction.

The charge stocks of the presen-t invention are lubricating oil petroleum hydrocarbon distillate fractions boiling within the range of about 420 to about 800 F, at a pressure of l0 mm, of mercury and containing from about to 40 weight percent of parailnic wax components.

The dewaxing solvent to be employed is preferably a mixture of a precipitating type solvent with a diluent type solvent. Thus, the precipitating type component may be an aromatic compound. Thus, ketones such as acetone, methylethylketone, methyl-n-propyl ketone, diethylketone, etc. and mixtures thereof may be employed in connection with an aromatic diluent type solvent such ice as benzene, toluene, xylenes,.etc. and mixtures thereof. As another example, a precipitating type solvent such as ethylene dichloride may be employed in conjunction with a diluent type component `such as benzene, chloroform,

carbon tetrachloride, etc. and mixtures thereof. As a,

further example, the precipitating component may be furfural and the diluent component may be an aromatic compound such as benzene.

In general, the dewaxing solvent will contain a major amount of the precipitating type component and a minor amount of the diluent type component. As is known to those skilled in the art, the ratio of precipitant type cornponent to diluent type component will be dependent, in large measure, upon the dewaxing temperature to be employed, the characteristics of the charge stock to be dewaxed and the desired product quality. Thus, a workman skilled in the art may readily select a suitable precipitating type component and a suitable diluent type component to produce the desired product from a given charge stock. As a specific example, a mixture of about 60 to S0 volume percent of methylethylketone with from about 40 to 20 volume percent of an aromatic hydrocarbon such as benzene or toluene may be employed for treating the feed stocks of the present invention.

Dewaxing operations are preferably conducted at a temperature within the range of about 10 to about +20 F. and, more preferably, at a temperature Within the range of about 10 to about l-5 F. Wax deoiling or wax fractionation operations are preferably conducted at a temperature within the range of about 0 to about 120 F. `which is higher than the dewaxing temperature employed. Thus, when dewaxing operations are conducted at a temperature of `about 10 to about +5 F.,'it is preferable to conduct deoiling operations at a temperature within the range of about -}-l0 to +20 F., depending upon the desired quality of deoiled wax.

The invention will be further illustrated with respect to the accompanying drawings wherein the sole FIGURE is a schematic ow sheet showing the manner in which dewaxing and deoiling operations are conducted in accordance with the present invention.

With reference to FIG. l, a waxy lubricating oil fraction from a suitable source (not shown) such as a distillate fraction, a raiiinate fraction, etc. is charged by way of a line 10 containing a pump 11 to a chilling zone 12, the feed stock being charged to the chilling zone 12 in admixture with a suitable dewaxing solvent introduced into the system by way of a solvent charge line 14 controlled by a valve 15 leading to the feed stock charge line 10. i

The solvent mixed with the feed stock 10 by way of the line 14 is preferably a wet solvent containing less than about 3 volume percent of water. The amount of solvent to be employed should preferably be such that a dewaxed oil having desired predetermined physical properties for alubricating oil base stock including a desired pour point and viscosity index is obtained in maximized yield at a maximized filtration rate. Thus, by way of specific example, for a distillate feed stock boiling with in the range of about 440 to 750 F. at a pressure of l0 mm. of mercury and having a specific gravity of about 29 API, apour point of about 115 F., and a viscosity of about l40(SSU/130 F.), about 21/2 volumes of a mixture ofv about 65 volume percent of methylethylketone with about 35 volume percent of toluene may be employed to provide a dewaxed oil having a pour point of about 10 F. and a viscosity index of about 83.

Within the chilling zone 12 the mixture of feed stock and solvent may be chilled to a suitable dewaxing temperature, such as a temperature of about `0 F. whereby there is formed a slurry of wax crystals associated with oil and solvent in a mother liquor consisting of oil and solvent. The slurry, to readily flow, should contain not more than about 50 volume percent of crystals. The slurry is discharged from chilling Zone 12 by way of a line 16 leading to a turbulent isothermal tiltration zone 18. A recycle fraction obtained in a` manner to be described is charged to the slurry line 16 by way of a recycle line 20 controlled by a valve 2'1. While the turbulent isothermal filtration zone may be of any desired construction, it is preferably a zone containing line llter of the type disclosed in copending Moore and Royder application Serial No. 643,096, tiled February 28, 1957, now U.S. Patent No. 2,914,456'.`

In the turbulent isothermal filtration zone 18, a suitable amount ofthe mother liquor (e.g., about 20 to 60 volume percent of the slurry) is separated to thereby provide a mother liquor iiltrate fraction and a concentrated slurry fraction. It is desirable that the amount of filtrate withdrawn should be such that the solids content of the concentrated slurry fraction is not so excessive as to impair the ilowability of the concentrated slurry. Accordingly, it is preferable Athat the amount of slurry withdrawn be such that the concentrated slurry fraction contains from about 30` to 60 volume percent of solids.

The filtrate fraction, which is a solution of dewaxed oil in solvent, is withdrawn from the tiltration zone y18 by way of a line 22 leading to suitable recoveryy facilities (not shown) for separating the dewaxed oil from the dewaxing solvent.

The concentrated slurry fraction is discharged from the iiltration zone 13 by Way of a line 24 leading to a second iltration zone 26. The line 24 may, if desired,

pass through a heating zone 23 for a purpose tobe described. Prior to introduction into the Zone 26,'the

concentrated slurry fraction is diluted with a dry, de-

waxing solvent at the slurry temperature, the dry solvent,

which may contain up to about l percent of water, being introduced by way of a charge line 28 controlled by a valve 29 leading to the line 24. Although the amount of dry solvent to be employed may be varied within comparatively Wide limits, it is generally preferable to employ from about 50 to 150 volume percent of solvent, based on the total amount of wet solvent charged by Way of the line 14. Still more preferably, from about 80 to 120 volume percent of dry solvent will be employed. The thus-diluted slurry fraction is separated into a second concentrated slurry fraction in the zone Z6 which is discharged by Way of a line 30 and into a filtrate fraction which is Withdrawn by way of the line 20 for recycle in the described manner. The amount of filtrate separated from the slurry in the zone 26 will again be such that the slurry is concentrated without impairing its ability to iiow. Alternately, all or a part of the filtrate fraction from the zone 26 may be discharged from the system for a purpose to be described by Way of a discharge line 25 controlled by a valve 27. Filtrate discharged by the line 25 may be charged to a zone for the separation of oil and solvent (not shown) which may be the same or different from the separation zone for the -filtrate 22.

From the foregoing description, it will be observed that, in accordance with this embodiment of the present invention, two iiltration zonesl are employed in series, wet solvent being added to the charge stock for the iirst filtration zone of the series and dry solvent being added to the feed stock for the second filtration zone.

When a dewaxing operation is conducted in this fashion, there is a substantial reduction in the amount of solvent required. Thus, for the charge stock of FIG. l, about 75 volume percent of dewaxed oil may be recovered from waxy oil while employing a total solvent circulation for the dewaxing step of about 2.5 barrels of solvent per barrel of feed stock. This constitutes a reduction of solvent circulation rate of about percent as compared with the amount of solvent required to obtain an equivalent quantity of dewaxed oil employing a one-stage rotary or line filter operation.

Returning again to the drawing, the concentrated slurry fraction 30 may be treated to recover deoiled Wax therefrom, When this is to be done, the slurry 30 may be mixed with a recycle fraction 38, to be described, and the mixture `may be warmed to .about 0 to 100 F. depending on desired Wax quality (e.g., about 30 F.) in a Warming zone 32. The warmed slurry is discharged from the warming zone 32 by way of a line 34 leading to a deoiling line filtration Zone 36. As a consequence,

the slurry may contain about l0 to 20 percent of crystal lized wax in a mother liquor containing -about l0 to 20 volume percent of oil. About l5 to 25 volume percent of the mother liquor may be removed in the filtration zone 36 and discharged therefrom lby way of a discharge line 42 controlled by `a valve 43. The thus-removed mother lliquor constitutes a ysolution of high pour point dewaxed oil in solvent which may be charged to suitable oil and solvent recovery zones (not shown) or used as recycle to the dewaxing operation. In this latter situation, the iilti'ateis recycled to the charge line 10 by Way of a recycle line 44 controlled by a valve 46. The concentrated slurry fraction from the zone 36 is discharged therefrom by Way of a line 48 leading to a rotary tilter 40 of .any suitable construction. The fraction, `after being diluted vwith an amount of solvent added by way of line 49 suiiicient to provide an easily lterable slurry is charged to the rotary filtration zone 40. Within the rotary filtration zone 4t) the wax is separated from the mother liquor to form a Wax filter cake which is washed with fresh solvent introduced by Way -of 'a charge line S0. The washed, deoiled Wax, together with entrained solvent, is discharged from the rotary liltration'zone 40 by way of aline 52 leading to a recovery zone (not shown). The mother liquor-'filtrate is recycled to the line 30 for the AWarming zone 32 by way of the line 3S in the described manner.

By way of specific example of the manner in which a paraiiinic lubricating oil may be dew-axed in accordance with the present invention, a mixture of about l0 volumes of a Wet (3% water) dewaxing solvent (a mixture of 65 volume percent of rnethylethylketone with 35 volume percent of toluene) with about 10 volumes of a waxcontaining lubricating oil feed stock (8O volume percent ofoil and 20 volume percent of Wax) may be chilled to a temperature of about 0 F. in the chilling zone 12 to precipitate the Wax. The slurry may be mixed with l0 volumes of a recycle slurry 20 containing Vabout 92.3 percent solvent and about 7.7 percent oil in the line 16 land the resultant mixture may be charged to the tirst line lter Zone 18. Within the zone 1S the mixture may be separated into about 5 volumes of a iirst concentrated slurry fraction containing about 34.6 volume percent of solvent, about 25.4 volume percent of oil and about 40 volume percent of Wax crystals and a iiltrate containing about 25 volumes of a rst filtrate fraction containing about 70 volume percent of solvent and about 30 volume percent orf oil. The iirst filtrate fraction may be charged to 'a suitable recovery zone (not shown) of any desired conventional construction wherein the oil and solvent may ybe separated to provide make-up solvent and a low pour point dewaxed oil product.

About l0 volumes of dry solvent charged by way of the charge line 218 are :added to the first concentrated slurry fraction 24 and the resultant mixture is charged to the second line iilter zone 26. Within the second line iilter zone 26, the charge mixture is separated into l0 volumes of the recycle filtrate fraction in line 20 described above `and 5 volumes of Va second concentrated slurry fraction in line 30 containing Vabout 40 volume percent of wax crystals in a mother liquor containing about 50 volume percent of solvent and about l0 volume percent of oil. The second concentrated slurry fraction in line 30 may go to a wax-solvent recovery system (not shown) or be further processed in the wax-deciling unit to recover deoiled Wax in the described manner.

Thus, the volumes of concentrated slurry may be mixed with about 14.4 volumes lof recycle fraction from the line 3S to provide 19.4 volumes of a mixture containing about 87 volume percent solvent, about 2.3 percent of oil and about 10.7 percent of wax. The mixture is warmed to above 0 F. and turbulently isothermally filtered in the zone 36 to provide a filtrate fraction 42 and 3.2 volumes of a concentrated slurry fraction containing about 49.5 volume percent solvent, about 1 percent oil and about 49.5 percent wax. The fraction in the line 4S is then mixed with about 14.4 volumes of solvent to provide a slurry for the rotary filter 40 having about a :1 ratio of liquid to wax crystals. On rotary filtration of this slurry, a wax filter cake is obtained which is washed with about 1.6 volumes of solvent, whereby about 3.2 volumes of a filter cake containing about 50 volume percent of Wax, about 50 percent of solvent (total oil content below about 0.3 percent) and 14.4 volumes of the recycle filtrate fraction containing about 93.5 v-olume percent solvent and about 0.5 percent oil.

Numerous advantages are obtainable through the provision of the process of the present invention. Thus, as mentioned above, a maximized recovery of dewaxed oil may be obtained with a minimized solvent circulation rate. In addition, several grades of dewaxed oil may be produced simultaneously. Thus, for example, a low pour point oil (0 to 10 F.), a medium pour point oil (30 to 70 E), and a high pour point oil (30 to 70 F.) may be simultaneously obtained by sep-arately recovering lthe oil in the filtrate fractions 22, 25, and 42V, respectively. In this situation, the slurry charged to the Zone 26 will be heated in a warming zone 23 provided in the charge line 24 for the purpose of Warming the slurry to a temperature sufficient to prov-ide a medium pour point oil having a desired pour point. Still further, intermediate grades of lubricating oil may be produced by selectively discarding all or a portion of either the filtrate fraction 25, the filtrate fraction 42, or both. In this situation, of course, the amount of normally recycled filtrate (as described above) which is withdrawn from the system is replaced with an equivalent amount of fresh solvent.

As another example, an unexpected or temporary change in feed stock composition, which would normally result in an off-specification dewaxed oil, may be compensated for by selective ltrate discard, as set forth above.

Having described my invention, what is claimed is:

1. in a continuous method for the low temperature dewaxing of a paraffinic lubricating oil fraction wherein a solvent is employed, the improvement which comprises the steps of mixing the feed stock with fresh solvent, chilling the mixture to a temperature sufficient to form an initial slurry of crystallized oil-containing wax in a mother liquor ycomprised of dewaxed oil `and solvent, passing the resultant slurry through a first turbulent isothermal filtration zone and turbulently isothermally removing from `about 20 to 60 volume percent of said mother liquor contained therein to provide a first filtrate fraction and a first concentrated slurry fraction, recovering dewaxed oil from said first filtrate fraction, adding to said first concentrated slurry fraction an amount of fresh solvent substantially equivalent to the amount of mother liquor recovered from said first filtrate fraction to thereby form a diluted first slur-ry. heating said diluted first slurry to a temperature greater than that of said rst turbulent isothermal filtration zone, passing said heated first slurry through at least a second turbulent isothermal filtration zone and turbulently isothermally removing 'from about 20 to 60 volume percent of the mother liquor therefrom to provide a Second filtrate fraction and a second concentrated `slurry fraction land recovering from said second filtrate fraction a dewaxed oil having a pour point greater than the pour point of the dewaxed oil recovered from said firs-t filtrate fraction.

2. In a continuous method for the low temperature dewaxing of `a paraffinic lubricating oil fraction wherein a solvent is employed, the improvement which comprises the steps of mixing the feed stock with fresh solvent, chilling the mixture toa temperature sufiicient to form an initial slurry of crystallized oil-containing wax in a mother liquor comprised of dewaxed oil and solvent, passing the resultant slurry through a first turbulent isothermal filtration zone and turbulently isothermally removing from about 20 to 60 volume percent of said mother liquor contained therein to provide a first filtrate fraction Iand a first concentrated slurry fraction, recovering dewaxed oil from said first filtrate fraction, adding to said first concentrated slurry fraction an amount of fresh solvent substantially equivalent to the amount of mother liquor recovered from said first ltrate fraction, to thereby forma diluted first slurry, heating said diluted first slurry to a temperature greater than that of said first turbulent isothermal filtration zone, passing said heated first slurry through at least a second turbulent isothermal filtration zone and turbulentily isothcrmally removing from about 20 to 60 volume percent of the mother liquor therefrom to provide a second filtrate fraction and a second concentrated slurry fraction, recovering from said second filtrate fraction a dewaxed oil having a pour point greater than the pour point of the dewaxed oil recovered from said first filtrate fraction, mixing a fourth filtrate fraction, as hereinafter defined, with said second concentrated slurry fraction to provide a diluted second slurry fraction, warming said second diluted slurry fraction to an extent sufiicient to dissolve a desired amount of the oil initially contained in said Wax into said mother liquor, passing said warmed second slurry through a third turbulent isothermal filtration zone and turbulently isothermally removing from about 20 to 60 volume percent of the mother liquor therefrom to provide a third filtrate fraction and a third concentrated slurry fraction, recovering from said third filtrate fraction a dewaxed oil having a pour point greater than the pour point of the dewaxed oil recovered from said second filtrate fraction, `diluting said third filtrate fraction with solvent, charging said diluted slurry fraction to a rotary filtration zone and there resolving it into a waxy filter cake fraction and said fourth filtrate fraction as aforesaid.

lReferences Cited in the file of this patent UNITED STATES PATENTS 2,083,578 Roberts June 15, 1937 2,161,569 Gross June 6, 1939 2,486,014 Evans Oct. 25, 1949 2,612,466 Kiersted et al Sept. 30, 1952 2,730,242 Samuel lan. 10, 1956 2,734,849 Gross et al. Feb. 14, 1956y 2,820,070 Bennett et al. Ian. 14, 1958 2,848,519 Corneil et al. Aug. 19, 1958 2,914,456 Moore et al. Nov. 24, 1959 

1. IN A CONTINUOUS METHOD FOR THE LOW TEMPERATURE DEWAXING OF A PARAFFINIC LUBRICATING OIL FRACTION WHEREIN A SOLVENT IS EMPLOYED, THE IMPROVEMENT WHICH COMPRISES THE STEPS OF MIXING THE FEED STOCK WITH FRESH SOLVENT, CHILLING THE MIXTURE TO A TEMPERATURE SUFFICIENT TO FORM AN INITIAL SLURRY OF CRYSTALLIZED OIL-CONTAINING WAX IN A MOTHER LIQUOR COMPRISED OF DEWAXED OIL AND SOLVENT, PASSING THE RESULTANT SLURRY THROUGH A FIRST TURBULENT ISOTHERMAL FILTRATION ZONE AND TURBULENTLY ISOTHERMALLY REMOVING FROM ABOUT 20 TO 60 VOLUME PERCENT OF SAID MOTHER LIQUOR CONTAINED THEREIN TO PROVIDE A FIRST FILTRATE FRACTION AND A FIRST CONCENTRATED SLURRY FRACTION, RECOVERING DEWAXED OIL FROM SAID FIRST FILTRATE FRACTION, ADDING TO SAID FIRST CONCENTRATED SLURRY FRACTION AN AMOUNT OF FRESH SOLVENT SUBSTANTIALLY EQUIVALENT TO THE AMOUNT OF MOTHER LIQUOR RECOVERED FROM SAID FIRST FILTRATE FRACTION TO THEREBY FORM A DILUTED FIRST SLURRY, HEATING SAID DILUTED FIRST SLURRY TO A TEMPERATURE GREATER THAN THAT OF SAID FIRST TURBULENT ISOTHERMAL FILTRATION ZONE, PASSING SAID HEATED FIRST SLURRY THROUGH AT LEAST A SECOND TURBULENT ISOTHERMAL FILTRATION ZONE AND TURBULENTLY ISOTHERMALLY REMOVING FROM ABOUT 20 TO 60 VOLUME PERCENT OF THE MOTHER LIQUOR THEREFROM TO PROVIDE A SECOND FILTRATE FRACTION AND A SECOND CONCENTRATED SLURRY FRACTION AND RECOVERING FROM SAID SECOND FILTRATE FRACTION A DEWAXED OIL HAVING A POUR POINT GREATER THAN THE POUR POINT OF THE DEWAXED OIL RECOVERED FROM SAID FIRST FILTRATE FRACTION. 